A diabolist can convert all elemental spells to Hellfire.
A Hellfire ray deals half fire, half unholy damage
The infernal bloodline has a power that deals fire damage, with aditional Shaken to good.
A pit fiend duke has a hellfire breath, half fire, half unholy.
There might be more references.
I would assume that Hellfire is half fire, half unholy, but I can't find a definitve explanation.
Agree, disagree, have a better suggestion?
Thanks,
The definition of Hellfire is in "Pathfinder Chronicles: Book of the Damned Vol.1 - Princes of Darkness", page 5 (the same book the Diabolist PrC is in):
Hellfire is treated as normal fire, but deals half fire damage and half damage from unholy energy. Damage dealt by hellfire is known as hellfire damage. Evil-aligned creatures and creatures with the evil subtype take no damage from the unholy energy, but good-aligned beings and those with the good subtype take double the normal damage from it. Creatures under the effects of spells like protection from evil are unaffected by this unholy energy, though they may still take fire damage.
Excellent, thanks!